| The high sensitivity of Rydberg atoms to external fields as well as interactions among them leads to strong a enhancement of optical nonlinearities in ultracold Rydberg gases. Here we present a many-body density-matrix approach that allows to describe such problems under EIT conditions. We find a strong influence of both the effects of an external electric field as well as strong van der Waals interactions on the optical response of an ultracold Rydberg gas, and determine the corresponding optical nonlinearities. |
|